Fibrous articles and electrode systems

ABSTRACT

An apparatus including a body having dimensions suitable as an electrode component of an electrical storage device, the body having a fibrous form comprised of a moiety of the general formula:  
     (M a ) x (Y b ) y ,  
     wherein M is one or more metals (i.e., a is greater than or equal to one) selected from Groups IV through IX of the Periodic Table of the Elements. Examples include, but are not limited to, ruthenium, iridium, and manganese. Y includes one or more heteroatoms (i.e., b is greater than or equal to one) selected from oxygen, nitrogen, carbon, and boron. Subscripts x and y represent the valence state of the cation and anion, respectively.

[0001] This is a divisional of U.S. patent application Ser. No.09/727,018 filed on Nov. 28, 2000, entitled “Fibrous ElectrodeMaterials”.

[0002] This invention was made with Government support under contractDASG60-00-M-0148 awarded by the U.S. Army Space and Missile DefenseCommand. The Government has certain rights in the invention.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The invention generally relates to the field of methods for andproducts of manufacturing component parts in energy storage devices andmore particularly, to high surface area electrodes for supercapacitorapplications.

[0005] 2. Description of Related Art

[0006] In general, electrochemical capacitors are capacitive energystorage devices based on double-layer capacitance or pseudocapacitance.The potential, power density and cycle life of electrochemicalcapacitors are generally two orders of magnitudes higher than those ofrechargeable batteries. As compared with batteries, electrochemicalcapacitors can be characterized as having low energy density, high powerdensity and a high cycle life. Further, in an electric circuit, anelectrochemical capacitor behaves more like a classic dielectriccapacitor than a battery, hence its name.

[0007] The requirement of high energy and power density of anelectrochemical capacitor intrigues development in miniaturization andweight reduction. The component parts of an electrochemical capacitorgenerally include at least two electrodes, electrolyte, and a separator.The material of the electrode is typically a key element. One approachto increase energy and power density of an electrochemical capacitor isto increase the accessible surface area of the electrodes. Generally,the pore size of the electrode material must be large enough to allowelectrolyte access into the pores, yet small enough to provide a highsurface area per volume or per weight of the electrode material.Lowering the internal resistance (e.g., resistivity of the electrodematerial or interface resistance between electrode constituents) of theelectrode material is also a key point toward increasing conductivityand power density of electrode materials. A contact resistance betweenan electrode and the electrolyte and/or current collector can alsoincrease the resistance of the capacitor.

[0008] There are four basic types of electrode materials forelectrochemical capacitor applications. Activated carbon or foamrepresents one type of electrode material, as disclosed by U.S. Pat. No.5,601,938. Typical capacitance obtained from an electric double layer isin the range of about 20-40 mF/cm².

[0009] Certain transition metal oxides such as rubidium oxide (RuO₂) andiridium oxide (IrO₂) possess pseudocapacitance thus rendering metaloxides as a candidate for a second type of electrode material.Pseudocapacitance arises from highly reversible reactions, such asoxidation-reduction (“redox”) reactions, which occur at or near theelectrode surfaces. Capacitance of 150-200 mF/cm² have been observed forRuO₂ films. A specific capacitance of 380 F/g has been reported usinghigh temperature thermal treatment and 720 F/g with low temperaturethermal treatment. Low temperature treatment generally forms amorphoushydra-ruthenium oxide, which tends to crystallize at temperatures above100° C. Ruthenium electrode material also tends to be relativelyexpensive. In order to reduce the cost of the expensive ruthenateelectrode materials, bi-metal oxides or tri-oxides were studied, such aslead ruthenate systems having a formula A₂[B_(2-x)Pb_(x)]O_(7-y), whereA is lead (Pb) or bismuth (Bi); B is ruthenium (Ru) or iridium (Ir); xis greater than zero and less than or equal to one; and y is greaterthan zero and less than 0.5 as disclosed by U.S. Pat. No. 5,841,627.

[0010] The third type of electrode material is metallic bodies which aremechanically- or chemically-etched to provide a roughened surface and ahigh specific surface area, as disclosed by U.S. Pat. No. 5,062,025.High surface area metal electrodes are limited by electrochemicalstability. Metals are generally unstable in oxidizing environments,therefore their use is generally limited to the positive, reducingelectrode or anode.

[0011] The fourth type of electrode material is metal nitride. Metalnitrides are generally conductive and exhibit pseudocapacitance.Molybdenum nitride, for example, as pointed out at the SeventhInternational Seminar on “Double Layer Capacitors and Similar EnergyStorage Devices, Dec. 8-10, 1997, Deerfield Beach, Fla., exhibits highenergy density.

[0012] In addition to the different types of electrode materials, it hasbeen found that the electrical performance of devices based onelectrodes of consolidated powders is often limited by inter-particleelectrical resistance (e.g., internal resistance), and this requiresaddition of conductivity-enhancing additives such as metal fibers whichare themselves generally not capacitive. Consolidated powders typicallyhave a lower powder density per unit weight of capacitor. U.S. Pat. No.4,562,511 discusses carbon fiber electrodes. The mechanical strength ofthe electrode is high, and small type capacitors in various shapes areobtainable, furthermore capacitance per unit volume can be maderelatively large and internal resistance and leakage current can be maderelatively low.

[0013] It is desirable to provide a new type of electrode material withimproved mechanical strength, reduced internal resistance and leakagecurrent, and increased capacitance per unit volume. It is also desirablethat the new type of electrode material possess high surface area and adesirable pore size.

SUMMARY

[0014] The invention relates to an apparatus suitable as an electrode inan energy storage device, including an electrochemical capacitor. Theapparatus comprises a body having a fibrous form comprised of a moietyof the general formula:

(M_(a))_(x)(Y_(b))_(y),

[0015] wherein M is one or more metals (i.e., a is greater than or equalto one) selected from Groups IV through IX of the Periodic Table of theElements. Examples include, but are not limited to, ruthenium, iridium,and manganese. Y includes one or more heteroatoms (i.e., b is greaterthan or equal to one) selected from oxygen, nitrogen, carbon, and boron.Subscripts x and y represent the valence state of the cation and anion,respectively. The invention further relates to an apparatus such as anenergy storage device. In one embodiment, an energy storage deviceincludes an electrolyte between two electrodes of fibrous material.Advantages of the device described or as formed herein in terms ofelectrode properties and performance compared generally to prior artdevices include: (1) reduced internal resistance and leakage current ofthe supercapacitive device, therefore improving power density; (2)increased specific surface area of fibrous electrode material, thereforehigher energy density; (3) enhanced mechanical strength of theelectrode, therefore lowering the contact resistance.

[0016] Additional features, embodiments, and benefits will be evident inview of the figures and detailed description presented herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The features, aspects, and advantages of the invention willbecome more thoroughly apparent from the following detailed description,appended claims, and accompanying drawings in which:

[0018]FIG. 1 is a schematic flow of forming a body of fibrous materialaccording to an embodiment of the invention.

[0019]FIG. 2 is a schematic top side perspective view of a body that isan electrode according to an embodiment of the invention.

[0020]FIG. 3 is a schematic side view of an electrical storage deviceaccording to an embodiment of the invention.

[0021]FIG. 4 is a schematic side view of an electrical storage device ofa bipolar ultracapacitor.

DETAILED DESCRIPTION

[0022] In one embodiment, a method is disclosed. The method comprisessynthesizing polymeric precursors via organic acid modification andfabricating a fibrous material of the polymeric precursors. The fibrousmaterial is then fabricated into a body of fibrous material. The methodof making these fibrous electrode materials include forming whiskers,fibers, clothes, and other collections assembled in the form of fiberelectrodes. The method is suitable for forming electrodes for electricalstorage devices such as electrodes for electrochemical cells. Suchelectrical storage devices generally have both a high energy and a highpower density with the use of fibrous electrode materials. Such fibrouselectrode materials (e.g., nanostructure electrode materials) inelectrical storage device applications also show reduced resistanceproperties both internally (e.g., resistivity and interface resistancebetween electrode constituents) and externally (e.g., contactresistance) are disclosed with improved mechanical strength.

[0023] In another embodiment, an apparatus suitable as an electrode forelectrical storage device applications, including electrochemicalstorage devices, is disclosed. The apparatus includes a body havingdimensions suitable as an electrode component of an electrical storagedevice. The body is composed of a moiety of the general formula:

(M_(a))_(x)(Y_(b))_(y),

[0024] wherein M is one or more metals (i.e., a is greater than or equalto one) selected from Groups IV through IX of the Periodic Table of theElements. Examples include, but are not limited to, ruthenium, iridium,and manganese. Y includes one or more heteroatoms (i.e., b is greaterthan or equal to one) selected from oxygen, nitrogen, carbon, and boron.Subscripts x and y represent the valence state of the cation and anion,respectively. A plurality of such moieties are linked in a fibrous formthrough the modification of a polymeric fiber to form the body. Suchfibrous forms include, but are not limited to, a collection of whiskers,partial or continuous fiber weaves, clothes, or other collectionsassembled to form the electrode.

[0025] Suitable nanostructure electrode materials include nitrides,carbonitrides, oxycarbonitride and/or oxides and methods of fabricationthereof for supercapacitor applications. The electrodes disclosed havereduced internal resistance and leakage current. Such electrodes alsooffer high mechanical strength which may yield large capacitance perunit volume. One characteristic with respect to fibrous oxides,nitrides, oxynitrides and oxycarbonitrides electrodes according to theinvention is reduced resistance. Resistance may be divided intoindividual components. A contact resistance, R₁, between a currentcollector and electrode; a resistance, R₂, attributable to the electrodematerial itself (e.g., resistivity of electrode material); an interfaceresistance, R₃, between the constituents (e.g., particles) of theelectrode; and a resistance, R₄, attributable to the electrolyte (e.g.,the resistivity of the electrolyte material). The fibrous electrode ofthe invention show at least a reduced interface resistance, R₃. Thecontact resistance, R₁, may also be reduced due to the higher mechanicalstrength of the fibrous electrode material, therefore permitting theapplication of higher pressure to compress the electrode and therebyimprove the contact between electrode and current collector.

[0026] In one embodiment, the invention relates to a method for makingand product of nanostructure porous fibrous materials with high specificsurface area by utilizing a sol-gel related technology. In one sol-gelprocess, a precursor solution is subjected to hydrolysis, condensationand polymerization to yield a nanostructure gel. The structure of thegel can be built by controlling the coordination through theelectrophillicity of the ligand.

[0027] In another embodiment, the invention relates to a method formaking and product of nanostructure porous fibrous materials with highspecific surface area by amine polymerization. In one process, aprecursor solution is subjected to aminolysis to form a polymer.

[0028]FIG. 1 illustrates a representative process flow for forming abody of fibrous material according to an embodiment of the method of theinvention. Referring to block 110, in a first embodiment, polymericprecursors are prepared by modifying precursor solutions withunhydrolyzed organic acid or other organic ligands. In one example,metal alkoxides are condensed with unhydrolyzed organic acids, esters,or other organic ligands. Suitable metal alkoxides include those of thegeneral formula M(OR)_(x), where M is selected from one or more metals(e.g., double alkoxides) from the Groups IV through IX of the PeriodicTable of the Elements, such as rubidium (Ru), iridium (Ir), andmanganese (Mn); R is an alkyl group, having for example, one to eightcarbon atoms or carbon atom equivalents; and x is equal to the valencestate of the cation. Suitable organic acids include, but are not limitedto, 2-ethylhexanoic acid (2-EHA), benzoic acid. Organic esters are alsosuitable and include, but are not limited to, o-xylene-α,α′-diacetate.

[0029] The contemplated alkoxides, when combined with the organic acid,ester or other ligand and optionally water undergo hydrolysis andcondensation reactions to form a polymeric network. The organic acidligand, for example, can be used to hydrolyze the alkoxide and also achelating agent to link alkoxides together to form a generallynon-hydrolyzable chelation bonded polymeric network. Suitable moleratios of alkoxide to organic acid to water include n:1:0.3 ton:(n−2):1, where n is the valence of the metal. A general representationis:

[0030] Reaction (1) shows the reaction between the alkoxide and theorganic acid and, optionally, the alkoxide and water. Combining theproducts of reaction (1) produces a polymeric precursor (e.g., amonomer) in reaction (2). The polymeric precursor contains hydrolyzablemoieties for further polymerization (the terminal “—OR”), and anon-hydrolyzable moiety represented by the pseudo-carbonyl.

[0031] In a second embodiment, polymeric precursors are formed byaminolysis. In one example, metal alkylamides undergo aminolysis byreaction with an amine. Suitable metal alkamides include those of thegeneral formula M((N_(w)C_(x))R_(y))_(z), where M is selected frommetals from the Groups IV, V, and VI of the Periodic Table of theElements, rubidium (Ru), iridium (Ir), and manganese (Mn); R is an alkylgroup having, for example, one to eight carbon atoms or carbon atomequivalents; w is one to four; x is zero to three; y is the number ofalkyl groups bonded to each nitrogen and/or carbon; and z is the valencestate of the cation. Suitable amines are of the general formula R′NH₂,where R′ includes, but is not limited to, an alkyl of one to eightcarbon atoms or carbon atom equivalents.

[0032] The contemplated metal alkylamides, when combined with the amine,preferably in the absence of moisture or oxygen to discouragehydrolysis, undergo aminolysis to form the polymeric precursor (e.g.,monomer) and a polymeric network. A general representation is:

[0033] Upon forming the polymeric precursors, block 120 shows that suchpolymeric precursors may be fabricated into fibrous material, typicallyby extrusion or spinning. The fibrous material may be short whiskers onthe order of a few to several hundred microns to a continuous weavablesingle strand fiber.

[0034] Referring to block 130 in FIG. 1, the fibrous material istransformed into a body of fibrous material suitable for use as anelectrode for use in an electrical storage device. In one approach,“green” fibrous materials formed of polymeric precursors through asol-gel process or aminolysis are dispersed in a cellulose matrix inpreparing the body of fibrous materials. The approach is analogous tothat described in U.S. Pat. Nos. 5,080,963; 5,096,663; and 5,102,745.The green fibrous materials are dispersed in a fluid medium along withcellulose acting as a binder and matrix for the fibrous materials. Theresulting dispersion is then cast into a predetermined shape. Onepurpose of the cellulose is to permit the fabrication of a solid preformof an otherwise structurally unstable dispersion of fibrous materialwhere the preform can be shaped, stored, and otherwise handled prior tosubsequent processing. The cellulose provides a stable, althoughrelatively weak, physical structure which maintains the spatialrelationship of the dispersed fibrous materials. Cellulose, in its formsand modifications, is a desirable matrix material because it may becompletely volatilized at relatively low temperatures with little ashformation, is generally unreactive toward other components in thepreform, and is readily available. Cellulosic materials typically usedin the paper-making process are suitable. A person of skill in the artwill recognize the elements of the paper-making process in the foregoingdescription.

[0035] After the dispersion of high surface area fibrous materials andcellulose in a liquid is attained, the solids are collected, as on amat. Excess liquid may be removed, such as by pressing, and theresulting solid dispersion is dried (e.g., liquid is removed) to form abody of fibrous material, especially where it is to be stored prior tofurther treatment. The drying process may be performed in air, underelevated temperatures, or in a flowing gas. The mass also may becompacted under pressure to a greater or lesser extent. The dispersionmay be cast into a predetermined shape prior to, coincident with, orafter drying. It may be desirable to cast the dispersion into sheetswhich can then be rolled up and stored prior to subsequent treatment.The fibrous content of the dry preform may be as low as about 50 weightpercent and as high as about 95 weight percent, although typically itwill range from about 90 to about 95 weight percent.

[0036] In a second approach, fibrous materials formed of polymericprecursors through a sol-gel or aminolysis process are directly pressed,or cast into a sheet, or woven into cloths constituting the body in theabsence of a preform, or binder, or matrix. The green sheet or clothsare then subjected to a heat treatment in controlled atmosphere or inair.

[0037] Referring to block 140 of FIG. 1, following drying of the body ofpolymeric fibrous materials, the body is subjected to a sinteringprocess. The sintering process converts a portion, including the entireportion, of the polymeric fibrous material of the body from an organicmaterial to a substantially inorganic material. A suitable sinteringprocess is performed in gaseous ambient, such as, for example, in thepresence of oxygen and/or nitrogen for 5 to 20 hours. In one embodiment,the temperature is slowly stepped toward the final desired temperature,residing at the final temperature for 4 to 6 hours. The sinteringconverts the polymeric fiber to moieties of fiber-like units ofgenerally inorganic (e.g., metal-heteroatoms) of oxides, nitrides,oxynitrides or oxycarbonitrides with desired crystallographic phases,which can be amorphous or crystalline.

[0038] By controlling the sintering atmosphere, oxide, carbide,oxycarbide and oxycarbonitride materials can be obtained. Oxide can beobtained by sintering air. Carbide and oxycarbide can be formed in N₂/H₂atmosphere or in methane. Ammonia gas will promote the formation of theoxynitride, oxycarbonitride and nitride.

[0039] Sintering at a low temperature (e.g., 200° C. to 400° C.)produces a generally amorphous phase fiber while sintering attemperatures than 400° C. (e.g., 700° C. to 900° C.) produces agenerally crystalline phase fiber. Crystalline phase fibers generallyhave a decreased surface area and higher conductivity compared toamorphous phase fibers.

[0040] In addition to rendering the fibrous material generallyinorganic, the sintering process also renders the material porous. Inthe example of an alkoxide-based polymeric precursor shown as theproduct of reaction (2), the pseudo-carbonyl gives up its oxygen atomduring sintering leaving voids in the network. Similarly, in thealkamide-based polymeric precursor shown as the product of rection (4),the amine gives up its alkyl constituent R′ during sintering leavingvoids in the network.

[0041]FIG. 2 shows a body of the inorganic fiber material. Body 150 inthis example is formed in the shape of an electrode suitable in anelectrical storage device including an electrochemical device (e.g.,electrochemical capacitor). It is to be appreciated that the size anddimensions of any such electrode will primarily depend on the scale ofthe electrical storage device and the suitable applications of anelectrode as described herein should not be limited.

[0042] Referring to FIG. 2, body 150 is comprised of a plurality offibers 155 wound, weaved, or otherwise collected. Fibers 155 arecompressed to reduce the internal resistance of body 150 (R₂). In oneexample, a collection of weaved fiber materials or a single woven fibermaterial strand is assembled into a body of 0.5 inches and 0.1 grams ofelectrode materials is compressed by the application of approximately2,000 pounds per square inch (psi).

[0043]FIG. 3 shows an electrical storage device that is anelectrochemical device. Electrochemical device 200 includes electrodes150A and 150B disposed in a cell and separated by separator 230.Electrochemical device 200 also includes electrolyte 220. One example isan electrochemical cell in which an electrical current is produced bychemical reactions. Effecting a chemical change by passing an electricalcurrent or electrolysis are induced by application of a direct currentof electricity.

EXAMPLE 1 Synthesis of Spinable Polymer Precursors for Titanium Oxide orOxycarbonite

[0044] Polymer precursors are formed by reacting titanium alkoxide withcertain cross-linking agents. One example uses titanium isopropoxide,and the cross-linking organics of o-xylene-α,α′-diacetate,2-ethylhexanoic acid (2-EHA), benzoic acid, or other organic acids.

[0045] The carboxylic or carboxolate ligand hydrolyzes the titaniumalkoxide and acts as a chelating agent to link titanium alkoxidemolecules together. A small amount of water is added to hydrolyze theremaining alkoxide ligands to form a polymeric titanate. Using benzoicacid as the cross-linking organic acid the reactions and polymerstructure may be represented as follows:

[0046] In the above representation, a suitable mole ratio of titaniumalkoxide, benzoic acid, and water is 1:1:0.3.

[0047] Titanium isopropoxide is dissolved into isopropanol, followed byadding diluted benzoic acid in isopropanol under the stirring. Thesolution is heated to 80° C. and refluxed overnight. Water is thenintroduced and the solution refluxed for another two hours. The solutionis then heated to 130 to 150° C. under vacuum to remove solvent and formthe spinable polymeric precursor. The viscosity can be further adjustedby changing solvent content.

EXAMPLE 2 Fiber Made by Extrusion Process

[0048] Fibers obtained from spinning process are homogenous in diameter.Continuous fibers become possible by an extrusion process. Fiberformation is possible when viscosity of the solution is between about 1to 100 Pa-s. Solvent content and also the extrusion temperature canadjust the viscosity of the polymeric precursor. The diameter of thegreen fiber can be controlled by orifice diameter, extrusion rate andpick-up rate.

[0049] The extruded green fiber can be cured by at least two methods:UV-curing and thermal-curing. Fibers cured at 254 mm UV-light with 320μm/cm² intensity for 8 hours showed a sufficient cross-linking reaction.The green fiber is cured also at 180 to 250° C. in air for 8 to 12hours. After curing, the green fiber is converted from thermal plasticto thermal set.

[0050] The cured fiber can be sintered at a high temperature and theshape maintained. By controlling the sintering temperature, amorphous orcrystalline phase fibrous structures can be obtained.

EXAMPLE 3 High Power Density Supercapacitor by Using Ruthenium OxideFibers as Electrodes

[0051] Procedure for Making Ruthenium Alkoxide and Polymer.

[0052] Dissolve strictly anhydrous ruthenium chloride in proper amountof tolunene. Sodium metal is added to excess alcohol (e.g., ethanol,isopropanol) to produce sodium alkoxide. Then three equivalent sodiumalkoxide is added to ruthenium chloride under stirring. Heat andprecipitation is resulted after the addition. The precipitate which issodium chloride can be removed either by filtration or centrifuge. Thereaction equation is shown as below. $\frac{\begin{matrix}{{Na} + {{{ROH}--}{NaOR}} + H_{2}} \\{{NaOR} + {{{RuCl}_{3}--}{{Ru}({OR})}_{3}} + {{NaCL}\left( {{R = {C_{2}H_{{5 - \quad}\quad}}},{C_{3}H_{7 -}}} \right)}}\end{matrix}}{{Na} + {ROH} + {{RuCl}_{3}{{Ru}({OR})}_{3}} + {NaCl}}$

[0053] Ruthenium alkoxide from procedure A is modified withacetylacetone (aca) and/or 2-ethyl hexanoic acid (2-EHA) beforehydrolysis and polycondensation. The molar ratio of aca and 2-EHA toruthenium is about 0.5 to 2. After modification, water is added at amolar ratio of about 05. to 1 and the solution is heated and refluxedfor about 3 hours. After the polymer has been obtained, most of thesolvent was removed by heating in vacuo until the viscosity reaches anempirical value of 4 cm/min. at which the polymer flowed from top tobottom of a vial.

[0054] Fiber Drawing and Pyrolysis:

[0055] Polymeric fiber is fabricated by using both hand drawing andspinnete extruding. The obtained fiber is cured in an oven forstrengthening to avoid a large shape change in the later hightemperature furnace and heat treated in air at 550° C. for more thanthree hours to burn off the organic content.

[0056] Fabrication of Ultracapacitor

[0057] A schematic of an ultracapacitor is shown in FIG. 4.Ultracapacitor 300 is configured in a bipolar construction.Ultracapacitor 300 includes six capacitors 310A, 310B, 310C, 310D, 310E,and 310F, each with an electrode area of 1 to about 2.85 cm². Rutheniumoxide fibers were used as the electrode material, and 2.5 M to about 4.5M sulfuric acid was used as the electrolyte. Current collector 320 inone embodiment is a 0.25 mm thick Ti foil. Glass fiber filter disks325A, 325B, and 325C are used as the separators. The stack was sealedinside Teflon cylinder 330 with rubber o-rings 340 and aluminum endplates 350 and 360.

[0058] In the preceding detailed description, the invention is describedwith reference to specific embodiments thereof. It will, however, beevident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

What is claimed is:
 1. An apparatus comprising: a body having dimensionssuitable as an electrode component of an electrical storage device, thebody having a fibrous form comprised of a moiety of the general formula:(M_(a))_(x)(Y_(b))_(y), wherein M is a metal selected from at least oneof Groups IV through IX of the Periodic Table of the Elements, wherein ais greater than or equal to one, wherein Y includes a heteroatomselected from one of oxygen, nitrogen, carbon, and boron, wherein x isthe valence state of the cation, and wherein y is the valence state ofthe cation.
 2. The apparatus of claim 1, wherein M is selected from thegroup consisting of molybdenum, tungsten, hafnium, zirconium, ruthium,iridium, and manganese.
 3. The apparatus of claim 1, wherein the bodycomprises a plurality of fibers, each fiber comprising the moiety. 4.The apparatus of claim 3, wherein the plurality of fibers are combinedin a weave.
 5. An apparatus comprising: a first electrode and a secondelectrode disposed in a cell; and an electrolyte in fluid contact withthe first and second electrode, wherein each of the first electrode andthe second electrode comprises a body having a fibrous form comprised ofa moiety of the general formula: (M_(a))_(x)(Y_(b))_(y), wherein M is ametal selected from at least one of Groups IV through IX of the PeriodicTable of the Elements, wherein a is greater than or equal to one,wherein Y includes a heteroatom selected from one of oxygen, nitrogen,carbon, and boron, wherein x is the valence state of the cation, andwherein y is the valence state of the cation.
 6. The apparatus of claim5, wherein M is selected from the group consisting of molybdenum,tungsten, hafnium, zirconium, ruthium, iridium, and manganese.
 7. Theapparatus of claim 5, wherein the body comprises a plurality of fibers,each fiber comprising the moiety.
 8. The apparatus of claim 7, whereinthe plurality of fibers are combined in a weave.